Why Do Some Trees Hang On To Their Dead Leaves?

Why Do Some Trees Hang On To Their Dead Leaves?

December 23, 2015

Every winter, the deciduous forest becomes barren and skeletal – the trees bare and the forest floor covered in brown, dead leaves. A few evergreens scattered about are reminiscent of the lush green colors of summers, but the rest of the trees have shed their leaves for winter, with new buds ready to grow as soon as spring arrives. But there is an anomaly to this pattern of the deciduous forest – a group of trees that seem confused as to whether they are deciduous or evergreen. These trees, which include oaks and beeches, keep their dead leaves around for the entire winter – a phenomenon known as “marcescence” where plants retain dead parts that are normally shed.

White Oak

American Beech

So why do some trees exhibit marcescence while others don’t? This question has confused botanists for years, and a number of theories have developed.

One involves winter browsers, especially deer, which feed on the nutritious buds of deciduous trees during the cold months. The theory is that, because marcescence is most prominent in younger trees and on the lower branches of older trees, the dead leaves must deter browsing animals from eating the buds. Perhaps the dead tissue of the leaves is less nutritious or palatable to deer, saving the tree from having its buds stripped during winter.

Another theory is that marcescence allows trees to recycle nutrients more efficiently. This makes sense because dropped leaves begin to decay and recycle nutrients back into the soil as soon as they are on the ground, so by waiting until the spring growing season to drop their leaves, marcescent trees are enriching soil conditions at their roots at the optimal time.

Others reject that there is any real evolutionary benefit to marcescence, postulating that it is merely an innocuous trait leftover from the divergence of evergreen and deciduous trees in certain families, serving no benefit or harm to the trees. Perhaps this is the case, considering that beeches and oaks belong to the family Fagaceae, which also contains several evergreen genera.

Whatever the reason for their steadfast dead leaves, we can all appreciate the phenomenon of marcescence and the variety it adds to the winter forest. Other animals appreciate it too, using the leaves to hide from the winter wind and find shelter from the snow.